Aelurostrongylus abstrusus (Railliet, 1898) Cameron, 1927
(Figures 4-15 through 4-22)
ETYMOLOGY: Aeluro = cat and strongylus = round, plus abstrusus = hidden from view
SYNONYMS:Strongyluspusillus Mueller, 1890, Strongylusabstrusus Railliet, 1898, Strongylusnanus Braun & Luehe, 1909, Synthetocaulusabstrusus Railliet and Henry, 1907
HISTORY: This worm was originally found and described by Mueller (1890c) as Strongyluspusillus. In 1898, Railliet (1898b) changed the name to Strongylusabstrusus. Braun and Luehe (1909a) described a species from the cat that they named Strongylusnanus. In 1907, Railliet and Henry (1907a) erected the genus Sythetocaulus to include this worm. Cameron (1927) erected the genus Aelurostrongylus and concluded that the larva passed in the feces was capable of infecting mice, this work has never been duplicated.
GEOGRAPHIC LOCATION: This is a metastrongyloid nematode parasite of the cat around the world (Ash, Center et al., 1990; Charan et al., 1984; Gathumbi et al., 1991; Martinez et al., 1990; Naylor et al., 1984; Pennisi et al., 1995; Wilson-Hanson and Prescott, 1982).
LOCATION IN HOST: The adults live in the terminal respiratory bronchioles and alveolar ducts.
PARASITE IDENTIFICATION: The adult females are 9 to 10 mm long with a vulval opening which, unlike most nematodes, occurs near the anus. The males are smaller, being 4 to 6 mm long, and have a small bursa and relative short and stout spicules. The worms are less than a millimeter wide and have a dark brown to black appearance when observed in fresh tissue. Due to the small worms being deeply within the terminal respiratory bronchioles and alveolar ducts, it is difficult to remove entire worms by dissection. The females lay eggs that contain a single cell when laid anw which embryonate within the alveolar ducts and the surround alveoli. The larvae hatch from the eggs, are carried up the ciliary escalator, swallowed, and passed in the feces. The larvae of Aelurostronbylus abstrusus are quite active larvae which are easy to recover in the feces using a Baermann apparatus. The larva is approximately 360-390 um long and has a characteristic dorsal spine on the tail (Figs 4-15 to 4-17).
LIFE CYCLE: The life cycle of Aelurostrongylus abstrusus has been shown to involve a required snail intermediate host (Hamilton and McCaw, 1967). It has also been shown that mice which ingest the infected snail can serve as a paratenic host (Mackerras, 1957). Hobmaier and Hobmaier (1935) also showed that if the larvae from snails were fed to frogs, toads, snakes, lizards ducklings, chickens, or sparrows that the larvae could later be recovered from their tissues. Thus, it seems highly possible that cats become infected typically by the ingestion of infected mice or birds. Stockdale (1970) found that the females began to lay eggs as early as 25 days postinfection; larvae have been found in the feces after 39 days of being infected with third-stage larvae (Gerichter, 1949).
CLINICAL PRESENTATION AND PATHOGENESIS:Aelurostrongylus abstrusus is known to cause severe pulmonary disease with heavy infections (Stockdale, 1970) (Figs. 4-18 to 4-20). Cats infected with 100 larvae showed early radiographic changes 2 weeks after infection (Mahaffey, 1979). The most severe disease was noted 5 to 15 weeks after infection and presented as alveolar disease. Examination of experimentally infected cats followed for up to a year after infection revealed that there was neither pulmonary hypertension or associated right ventricular disease (Rawlings et al., 1980). Pulmonary arteries in experimentally infected kittens show disruption of the vascular endothelium and proliferation of the endothelial cells, and as early as 10 days after infection, there is disruption of the internal elastic lamina (Figs 4-21 to 4-22). Hypertrophy and hyperplasia of the medial and intimal walls of the pulmonary vessels caused complete occlusion of many of the vessels by 24 weeks after infection (Naylor et al., 1984).
Mild infections often present with only minimal signs, however, heavy infections can cause severe bronchopneumonia with cats having rapid, open-mouthed abdominal breathing (Vig and Murray, 1986). A retrospective study of 312 cases of cats with eosinophilia revealed that 2% of the cases were infected with Aelurostrongylusabstrusus, while the majority of cases, 20.5%, had eosinophilia as a result of flea-bite allergy dermatitis (Center et al., 1990). Hamilton (1963) reported on one cat that was presumed to have died as a result of its lungworm infection. The 6-month-old cat developed signs of respiratory disease when three-months0old and the disease persisted. During this three month period, the cat was observed to be coughing and sneezing with a muco-purulent discharge. As the disease progressed, the cat became dyspneic, anorexic, emaciated, and with hydrothorax.
TREATMENT: In cats infected with Aelurostrongylusabstrusus, treatment with fenbendazole (55 mg/kg daily for 21 days (Vig and Murray, 1986) or 20 mg/ kg daily for 5 days followed by a second 5 day treatment after a five day hiatus) has been reported to be successful (Smith, 1980). Treatment of 15 cats experimentally infected with Aelurostrongylus abstrusus with fenbendazole (50 mg/kg, once daily for three days) stopped the shedding of larvae in the feces by 14 days after treatment, but a few days later, the larvae reappeared in small numbers in the feces of the infected cats (Roberson and Burke, 1980). Published reports on the efficacy of ivermectin has not produced conclusive results (Blagburn et al., 1987). However, there is a report of treatment with ivermectin (200 µg/kg followed by a second treatment with 400 µg/kg) clearing a cat of the Aelurostrongylus abstrusus infection (Kirkpatrick and Megalla, 1987).
EPIZOOTIOLOGY: Cats probably most typically become infected by the ingestion of captured prey, e.g., small birds and rodents. Thus, to prevent infection it is probably necessary to restrict the hunting of cats.
HAZARDS TO OTHER ANIMALS: This parasite seems restricted to cats, and the stage passed in the feces is not infectious to other avian or mammalian hosts until after a period of development in a mullusc. Thus, it is unlikely that this worm would pose a threat to other animals in a clinic.
HAZARD TO HUMANS: None.
CONTROL/PREVENTION: Control would be by the prevention of hunting by cats. It is unlikely that the monthly heartworm preventatives approved for cats would have any effects on the development of this parasite in the cat.
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Figure 4-15. Aelurostrongylus abstrusus. First stage larva passed in the feces. The characteristic dorsal spine on the larval tail is not evident in this image.
Figure 4-16. Aelurostrongylus abstrusus. First stage larva passed in the feces showing a higher magnification of the kinked tail with a dorsal spine.
Figure 4-17. Aelurostrongylus abstrusus. First stage larva recovered in a tracheal wash from an infected cat stained with Dif-Quik.
Figure 4-18. Aelurostrongylusabstrusus. Lungs of an infected cat showing changes in the serosal surface.
Figure 4-19. Aelurostrongylus abstrusus. Higher view of lungs showing numerous areas of apparent consolidation.
Figure 4-20. Aelurostrongylus abstrusus. Radiograph of lungs of infected cat.
Figure 4-21. Aelurostrongylus abstrusus. Histological section of lung showing sections of adult worm along with eggs within the parenchyma in various sstages of development.
Figure 4-22. Aelurostrongylus abstrusus. Transverse sction through lung parenchyma showing the large number of eggs in the tissues in various stages of development and a few free first-stage larvae.